Light oil, which is used for a diesel engine as fuel, includes components that are solidified when temperature drops. The solidified fuel causes a clogging of a filter. The filter captures foreign objects contained in the fuel. High temperature fuel which becomes excessive in a common rail or a fuel injector is recirculated into an inlet of the filter to melt the solidified fuel. Alternatively, the solidified fuel is heated by a heater to be melted.
However, in a case that a filter is disposed at an outlet of a fuel pump, the pressure of fuel discharged by the fuel pump is higher than that of fuel recirculated. Thus, it is difficult to introduce the recirculated fuel toward the filter. For example, EP-0819844A2 shows that the recirculated fuel is introduced into an inlet of a filter which is disposed outlet side of the fuel pump. Thus, it is necessary to increase the pressure of the recirculated fuel in order to introduce the recirculated fuel into the filter, which causes an increase in pressure resistance of pipes and parts through which the recirculated fuel flows. Besides, in a case that the filter is heated by a heater, a heat source, an electric power source, and electric leads are needed, which increase a number of parts.